Did you make this instructable?

Yes but you'll have to put some though into how you wire them. The 2 things you'll need to know are the impedance of the original speaker (4,8,16 ohms) and the power output of the amp, or the power handling of the speaker. Then you'll either have to wire your speakers to present the same impedance or higher impedance as the original (its normally safe to go higher, but it's a bit risky to go lower) If you settle on a higher impedance network then the power output will be reduced, but if you use more sensitive drivers then it may actually be louder anyway. Say you wanted to replace an 8ohm speaker being driven with 100w with 4 smaller speakers, then you could use 4x8ohm speakers and wire them in as 2 parallel strings of 2, each string would have an impedance of 16ohms (8+8) but having them in parallel would half the resistance back down to 8 ohms. Each speaker would have to handle 25w. Another example would be to replace a 4ohm speaker with 4x16ohm wired in parallel, giving a net impedance of 4 ohms, or 2x8ohms in parallel. I'm sure you get the idea.

Probably not, if you play it by the numbers your likely to blow your speakers. What would be really useful to know is the power output of your amp, but as that is an unknown quantity your going to have to assume its about 8 watts, in this case your 4 small speakers would be trying to dissipate 2 watts each, which is 4 times their rated power, That said your amp may be putting out considerably less than 8 watts, and the small speakers are probably quite conservatively rated in which case you could probably get away with it. Assuming these small speakers are costing next to nothing you may as well give it a go and just be prepared to blow them. If you want to give it a go, wire them as 2 strings of 2 speakers